Holley Idle Feed Restrictor Mod

Originally Posted by brad07

i've had to deal with an engine like that.
you could watch it on the AFR gauge we use. very slighty throttle opening and the gauge would climb to to 16.5:1 and POP and the engine would stall.
2 thou on the IFR and the problem was solved. though it did mean taking half a turn from each idle mixture screw. (two corner idle, 1850)

though this was a last resort. as we'd had similar problems with the same modle of car caused by the ignition system so we went down that path first

Yes, that is the correct condition a larger IFR size will fix, just when the throttle plates are barely opened by the pedel. But, usually only on the edge of stalling, you had it bad....Also sounds like you did the correct upstep in the size too, because that is just about how much you need to take out of the idle misture screws.

My current engine, and probably 3 others are the only times I needed to do this. The others were not my engines.

I have the exact problem with a holley 4010 (750 cfm). The carb has annular boosters with a teriffic mid range and good top end. Can the IFR be modified on these carbs?

Originally Posted by 2800R

I have the exact problem with a holley 4010 (750 cfm). The carb has annular boosters with a teriffic mid range and good top end. Can the IFR be modified on these carbs?

Yes you can. I have one of theses carbs as well as the book. "Holley 4010 & 4011" by Mike Urich. This book has detailed pictures of your carb with labels showing what the different passages and restrictors are. According to this book, the idle feed restrictor is located in the booster cluster. If you remove your booster cluster and flip it upside down so that the brass emulsion tubes are pointing up, and look just a little bit further out from where the emulsion tubes emerge, you will see two brass restrictors. These are the idle feed restrictors. I must caution you though. If this is an older carb it may have either the idle air bleeds or antisiphon holes plugged. I had a booster cluster on mine that was idleing rough and I couldn't get it to tune up with the mixture adjustment screws. It tured out that one of the antisiphon holes was plugged. I could poke a piece of wire into the hole but it was plugged somewhere further inside the booster cluster which caused gas to slowly drip out of the cluster at idle. The air bleeds are similar and could also be plugged in a similar manner. I recommend you soak them in a really good solvent and blow out all the passages before you try drilling the idle feed restrictors. I hope it works out well for you.
Julian

Thanks,
I appreciate the info.